Two oxygen-responsive regulatory systems controlling numerous symbiotic genes in Bradyrhizobium japonicum were assayed in free-living cultures for their capacity to activate target genes under different oxygen conditions. NifA-and FixLJ-controlled target genes showed disparate relative expression patterns. Induction of NifA-dependent genes was observed only at oxygen concentrations below 2% in the gas phase, whereas that of FixLJ-controlled targets progressively increased when the oxygen concentration was lowered from 21 to 5, 2, or 0.5%. We propose that this reflects a response to a gradient of increasing oxygen deprivation as bacteria invade their host during root nodule development.

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This automated GHB assay is fully quantitative and allows the accurate measurement of GHB in serum and urine. It can be used as a rapid screening assay for the determination of GHB in intoxicated or overdosed patients.

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In order to investigate the binding properties of the antigen I/IIf from Streptococcus mutans, we analyzed the binding activity of five I/IIf derivatives expressed by I/IIf gene derivatives obtained by insertion of a kanamycin resistance marker. ELISA-derived binding assays showed that the derivatives containing both the N-terminal alanine-rich domain (A-region) and an A-region distal domain extending to amino-acid 766 were the most effective in binding biotinylated (Biot-) human salivary components (SAC) and Biot-epithelial cell membrane components. Sodium metaperiodate treatment of SAC inhibited these interactions, suggesting a binding specificity of the A-region distal domain for carbohydrate residues. All the I/IIf derivatives were found to bind Biot-type I collagen, Biot-laminin, Biot-keratin, and Biot-fibronectin, the derivatives containing the A-region but lacking the A-region distal domain exhibiting the highest binding levels. Sodium metaperiodate treatment of laminin had no effect on its binding to the derivatives, suggesting that carbohydrate residues of the ligand were not involved.